Too Much Body Fat Bad for Bones?

Oct. 31, 2008 -- A woman's body fat may play a role in her bone mineral content after menopause, a new study shows.

The study, presented this week in Chicago at the annual meeting of the American Dietetic Association (ADA), shows that postmenopausal women with a higher proportion of body fat tend to have lower bone mineral content.

That may sound confusing, if you've heard that bigger people tend to have stronger bones. But size doesn't tell the whole story; body composition also matters, according to researcher Kathryn Piehowski, RD, of Pennsylvania State University.

The take-home message: "Weight is good for bone [but] keep it lean," Piehowski tells WebMD.

Bone mineral content was better for women on the leaner side -- those with a lower proportion of body fat -- compared to women with a higher proportion of body fat.

The reason for that isn't clear from this study, but Piehowski notes that having a high proportion of body fat is associated with greater inflammation, which may increase bone breakdown.

None of the women in Piehowski's study had osteoporosis (dangerously weak bones) or osteopenia (weak bones that aren't as weak as osteoporotic bones). But it's not clear if any of the women would eventually get osteoporosis or osteopenia, since the study was a snapshot in time without long-term follow-up.

Keep in mind that a person's body composition isn't always obvious. For instance, a large person who's all muscle may not have a lot of excess body fat, while someone who looks slim may not have a lot of muscle.